Crack testing system, in particular using the dye penetration method or magnetic method.
The invention relates to a crack testing system using the dye penetration method or for magnetic crack testing, having an illumination unit, a device for applying testing material and an evaluation station.
Various crack testing methods are known in the prior artxe2x80x94generally, for magnetizeable test pieces, in particular those made from iron, use is made of a magnetic powder method in the case of which magnetic dye particles accumulate at cracks and the like in a magnetic field at the test piece and are then detected under illumination. The dye is frequently fluorescing, and the contrast is thereby improved.
For non-magnetizeable materials, it is customary to use a so-called xe2x80x9cblack powder methodxe2x80x9dxe2x80x94use is made of dye solutions which accumulate in the cracks because of surface phenomena and capillary phenomena and can then be detected there within the specific test period. Such methods are known, for example, from EP 0831 321.
In both methods, use has been made for illumination purposes of conventional lampsxe2x80x94such as mercury vapor lamps, gas discharge lamps, flashlamps and this, in particular, because fluorescing dyes, which are used with particular alacrity, are most excited in the UV or in the blue range of the visible spectrum. Conventional lamps, in particularxe2x80x94those having thermal emitters, undergo severe aging. Even after a few burning hours, the UV component of such lamps is greatly reduced. Since, in particular, the UV component of the lamps is required for the fluorescence excitation, in the case of the known crack testing systems the lamp power must be expensively monitored and readjusted. Continuously changing intensities of the illuminating light can cause substantial false displays in the currently customary optical detection methods via image processing, for which reason lamp monitoring is expensive. Thus, for example, a system for lamp checking in crack testing systems of the generic type has become known from DE-A-40 13 133.5.
It is therefore the object of the invention to create a crack testing system with lamp monitoring which is less expensive.
This object is achieved according to the invention by means of a crack testing system which has light-emitting diodes (LEDs) as illumination units.
Advantageous developments follow from the subclaims.
According to the invention, the following advantages, inter alia, are achieved thereby: LEDs are not subject to aging phenomenaxe2x80x94that is to say, the intensity of the emitted light remains constant and the emission spectrum is not subject to driftxe2x80x94that is to say, the previously required expensive lamp monitoring and readjustment of the same can be eliminated, and a substantial simplification of the system is achieved.
LEDs are of small size and can also be installed at inaccessible sites.
LEDs radiate little warmth, as a result of which it is possible eliminate cooling measures, or else precautionary measures which have been required in the case of lamps in order to avoid burning.
Because of their emission, LEDs can excite a dye for fluorescence/phosphorescence at specific absorption wavelengths, as a result of which in the event of the use of various dyes the latter can be excited individuallyxe2x80x94for example if part numbers have been applied with a specific dye, the dye of the crack testing material has a different fluorescence wavelength and both are to be detected by the optical detection system for the purpose of individualizing the parts to be tested.
LEDs can easily be optically coupled to optical conductors, which can easily be led to inaccessible sites.
It is advantageous to use LEDs which emit in the region from 200 to 970 nm, since the dyes to be used absorb here.
It is favorable that the LED voltage can be modulated, since an improved signal processing by a processor is possible thereby.
LEDs can be optically coupled to optical conductors which conduct the illuminating light in the system.
In a specific embodiment of the invention, it is also possible to make use of a light distributor which splits light from a light source and thus permits the use of only one light source for different light outlets, as a result of which it is possible to eliminate controlling a plurality of lamps, their maintenance etc., or to limit controlling to only a single light source.
It can be favorable that if the crack testing system has a processor for controlling the devices for optical image processing, said processor also controls the LED power supply.